Method of migrating stored data and system thereof

ABSTRACT

There is provided a storage system and a method of migrating a source data portion from a source logical volume to a destination range in a destination logical volume. The method comprises: configuring a source mapping data structure to comprise an entry associated with said source data portion and indicative of mapping between logical addresses corresponding to said source data portion and addresses corresponding to said source data portion and related to a physical address space; and, responsive to a migration command, configuring a destination mapping data structure to comprise an entry associated with said at least one destination range and comprising a reference to said entry in the source mapping data structure, said entry in the source mapping data structure to be used for mapping to said addresses related to said physical address space and corresponding to the source data portion and to the migrated data portion.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application relates to and claims priority from U.S. ProvisionalPatent Application No. 61/513,811 filed on Aug. 1, 2011 and isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The presently disclosed subject matter relates, in general, to datastorage systems and respective methods for data storage, and, moreparticularly, to migrating data in the storage system.

BACKGROUND

Minimizing the impact of data migrations on business operations is acritical part of storage management. Technology refresh requiringreplacement of older servers or storage arrays with new ones is themajor driver of physical data migration. Additionally or alternatively,either because of overall optimization considerations (e.g. CPU usage,memory availability, bandwidth, etc.) or because of configurationmodifications (e.g. related to changes in user's privileges, etc.), adecision may come to migrate an application, thus requiring migratingdata from one logical volume to another. Wide implementation of VirtualMachines and cloud technologies increases the need for data migrationbetween logical volumes.

The problems of migrating data in the storage systems have beenrecognized in the conventional art and various systems have beendeveloped to provide a solution, for example:

US Patent Application No. 2011/066597 (Mashtizadeh et al.) discloses amethod of migration persistent data of virtual machines. The methodincludes the steps of copying the persistent data at the source datastore to the destination data store, updating a bitmap data structureduring the copying step to indicate which blocks of the persistent datahave been modified during the copying step, identifying the blocks thathave been modified during the copying step using the bitmap datastructure, and copying the identified blocks to the destination datastore.

US Patent Application No. 2010/299666 (Agbaria et al.) discloses amethod for migrating a virtual machine (VM) in a computing environment.The method comprises receiving a request to migrate a VM executing on asource host to a destination host; defining a recovery point to whichthe VM is restored during recovery from a fault; and iteratively copyinga memory of the source host associated with the VM to the destinationhost. During the copying, the original state of each page in the memoryis preserved. At some point, the VM suspends executing on the sourcehost, copies state information associated with the VM to the destinationhost, and resumes executing on the destination host. If a fault isdetected on the source host, the VM is restored to the recovery pointusing preserved information.

US Patent Application No. 2007/192765 (Shimogawa et al.) discloses avirtual machine system managed by a current host OS virtually operatingon hardware. A spare host OS is activated by copying the current host OSto a prescribed memory device using a live migration function when thecurrent host OS is activated, notifies the spare host OS of a requestissued to the current host OS via a virtual machine monitor, changes astate of the spare host OS, and switches an OS for managing the virtualmachine system from the current host OS to the spare host OS, when thecurrent host OS is in an erroneous state.

US Patent Application No. 2009/125904 (Nelson) discloses migration of asource virtual machine (VM) hosted on a source server to a destinationVM on a destination server without first powering down the source VM.After optional pre-copying of the source VM's memory to the destinationVM, the source VM is suspended and its non-memory state is transferredto the destination VM; the destination VM is then resumed from thetransferred state. The source VM memory is either paged in to thedestination VM on demand, or is transferred asynchronously bypre-copying and write-protecting the source VM memory, and then latertransferring only the modified pages after the destination VM isresumed. The source and destination servers preferably share commonstorage, in which the source VM's virtual disk is stored; this avoidsthe need to transfer the virtual disk contents. Network connectivity ispreferably also made transparent to the user by arranging the servers ona common subnet, with virtual network connection addresses generatedfrom a common name space of physical addresses.

US Patent Application No. 2007/220121 (Suwarna) discloses a virtualmachine migrated between two servers. A method, at the first server,dismounts a volume on which all the files relating to the virtualmachine are stored, and which was previously mounted at the firstserver. The method, at the second server, mounts the volume on which allthe files relating to the virtual machine are stored, so that the secondserver can host the virtual machine. In this way, the virtual machinecan be migrated without having to copy all the files from the firstserver to the second server. The files relating to the virtual machineare stored on a storage-area network (SAN).

US Patent Application No. 2005/283564 (LeCrone et al.) discloses amethod and apparatus for migrating one or more data sets each having oneor more extents from one or more source logical devices to one or moretarget logical devices concurrently with interaction between theapplication and the data being migrated. A background operation copieseach extent from the source logical device to the target logical devicein a copy state. When a certain level of data has been copied, theextent is locked to assure synchronization of the data in the targetlogical device to the corresponding data in the source logical device.The status is changed to a mirrored state. When the extents for a dataset in a source logical device or in a group of data sets have beenmirrored, all the extents are changed to a diverted state. I/O requeststo the diverted extents thereafter are intercepted and processedaccording to whether they access an extent that is in the copy,mirrored, or diverted state.

U.S. Pat. No. 6,145,066 (Atkin) discloses a computer system including atransparent data migration facility (TDNff) to accomplish automatedmovement of data (migration) from one location to another in the system.A data migration program includes a main module to control the start ofa migration session when said application programs are using dataaccessed to and from the source volume, to migrate data from the sourcevolume to the target volume, and to end the migration session wherebythe application programs are using data accessed to and from the targetvolume. The data migration program includes a volume module to controlthe volumes during the migration session. The data migration programincludes a copy module to control the copying of data from the sourcemodule to the target module during the migration session. The datamigration program includes a monitor module for monitoring I/O transfersto the data volumes during the migration sessions. The computer systemmay have a plurality of operating systems associated with instances ofthe data migration program which allows for concurrent data migrations.The plurality of instances of the data migration program may also becontrolled in a master slave relationship. A migration session mayinclude a plurality of migration phases such as activation, copy,refresh, synchronize, redirect, resume and termination phases.

SUMMARY

In accordance with certain aspects of the presently disclosed subjectmatter, there is provided a method of migrating at least one source dataportion from a source logical volume Vsrc to at least one destinationrange in at least one destination logical volume Vdest thereby givingrise to at least one migrated data portion in said at least onedestination logical volume Vdest. The method comprises:

configuring a source mapping data structure DSsrc to comprise at leastone entry associated with said at least one source data portion andindicative of mapping between one or more contiguous ranges of addressescorresponding to said at least one source data portion in the sourcelogical volume Vsrc and one or more ranges of addresses corresponding tosaid at least one source data portion and related to a physical addressspace; and,

responsive to a migration command, configuring a destination mappingdata structure DSdest to comprise at least one entry associated withsaid at least one destination range and comprising a reference to saidat least one entry in the source mapping data structure DSsrc, said atleast one entry in the source mapping data structure DSsrc to be usedfor mapping to addresses related to physical address space andcorresponding to the source data portion and to the migrated dataportion.

The method can further comprise addressing a request related to saidmigrated data portion received by said destination mapping datastructure DSdest to said at least one entry in the source mapping datastructure DSsrc.

In accordance with further aspects of the presently disclosed subjectmatter, the destination mapping structure DSdest can be configured as adestination ordered mapping tree TRdest, wherein said at least one entryin the destination mapping structure DSdest is implemented as a leaf ofsaid destination mapping tree TRdest, said leaf bearing, upon receivingthe migration command, a reference to said at least one entry associatedwith said source data portion in the source mapping structure DSsrc.

In accordance with further aspects of the presently disclosed subjectmatter, the method can further comprise associating said at least onesource data portion with a multiple-reference indication indicative of anumber of migrated data portions in one or more destination volumes,said migrated data portions mapped to the addresses related to physicaladdress space with the help of said at least one entry associated withthe source data portion in the source mapping data structure. Theindication can be provided with the help of a reference counterassociated with the source mapping data structure DSsrc and with thedestination mapping structure DSdest.

The source mapping structure DSsrc can be further configured as a sourceordered mapping tree TRsrc, wherein said at least one entry in thesource mapping structure DSsrc is implemented as a leaf of the treeTRsrc. The method can further comprise associating said leaves in thesource and the destination mapping trees with a multiple-referenceindication indicative of a number of migrated data portions in one ormore destination volumes, said portions mapped to the addresses relatedto physical address space with the help of said leaves.

In accordance with further aspects of the presently disclosed subjectmatter, the method can further comprise: responsive to a write requestrelated to said at least one source data portion, providing an atomicoperation, said atomic operation comprising:

assigning a new range of addresses related to physical address space fornew data to be destaged;

updating said at least one entry in the source mapping structure DSsrcto map between one or more contiguous ranges of addresses correspondingto said at least one source data portion in the source logical volumeVsrc and said new range of addresses related to physical address space;and

updating said at least one entry in the destination mapping structureDSdest to map between said at least one destination address range andaddresses related to physical address space and referred to, beforeupdating, via said at least one entry in the source data structureDSsrc, wherein, upon updating, said mapping is provided withoutreferencing to the source mapping structure.

In accordance with further aspects of the presently disclosed subjectmatter, the method can further comprise: responsive to a request todelete said at least one source data portion, providing an atomicoperation, said atomic operation comprising:

deleting said at least one entry in the source mapping structure DSsrc;

updating said at least one entry in the destination mapping structureDSdest to map between said at least one destination address range andaddresses related to physical address space and referred to, beforeupdating, via said at least one entry in the source data structureDSsrc, wherein, upon updating, said mapping is provided withoutreferencing to the source mapping structure; and

updating the value of multiple-reference indication associated with saidat least one migrated data portion.

In accordance with further aspects of the presently disclosed subjectmatter, the method can further comprise: responsive to a write requestrelated to said at least one migrated data portion, providing an atomicoperation, said atomic operation comprising:

assigning a new range of addresses related to physical address space fornew data to be destaged;

updating said at least one entry in the destination mapping structureDSdest to map between said at least one destination address range andsaid new addresses related to physical address space and correspondingto the migrated data portion, wherein said mapping is provided withoutreferencing to the source mapping structure; and

reducing by one the value of multiple-reference indication associatedwith said at least one source data portion.

In accordance with other aspects of the presently disclosed subjectmatter, there is provided a storage system comprising a plurality ofphysical storage devices constituting a physical storage space andcontrolled by a plurality of storage control devices constituting astorage control layer, wherein the storage control layer is operable toenable migrating at least one source data portion from a source logicalvolume Vsrc to at least one destination range in at least onedestination logical volume Vdest thereby giving rise to at least onemigrated data portion in said at least one destination logical volumeVdest. The storage control layer further comprises: a source mappingdata structure DSsrc configured to comprise at least one entryassociated with said at least one source data portion and indicative ofmapping between one or more contiguous ranges of addresses correspondingto said at least one source data portion in the source logical volumeVsrc and one or more ranges of addresses corresponding to said at leastone source data portion and related to a physical address space; and adestination mapping data structure DSdest configured to comprise atleast one entry associated with said at least one destination range andindicative of mapping between said at least one destination range andone or more ranges of corresponding addresses related to the physicaladdress space;

wherein said storage control layer is further operable to configure,responsive to a migration command, said at least one entry in thedestination mapping data structure DSdest to comprise a reference tosaid at least one entry in the source mapping data structure DSsrc, saidat least one entry in the source mapping data structure DSsrc isconfigured to be used for mapping to the addresses related to physicaladdress space and corresponding to the migrated data portion.

In accordance with further aspects of the presently disclosed subjectmatter, the system can further comprise a plurality of virtual machines,wherein the logical volumes Vsrc and Vdest are associated with differentvirtual machines.

In accordance with further aspects of the presently disclosed subjectmatter, the storage control layer can be further configured to provideassociating said at least one source data portion and said at least onemigrated data portion with a multiple-reference indication indicative ofa number of migrated data portions in one or more destination volumes,said migrated data portions mapped to the addresses related to physicaladdress space with the help of said at least one entry associated withthe source data portion in the source mapping data structure.

In accordance with further aspects of the presently disclosed subjectmatter, the source and/or the destination mapping structures can beconfigured as ordered mapping trees with the leaves associated with amultiple-reference indication indicative of a number of migrated dataportions in one or more destination volumes, said portions mapped to theaddresses related to physical address space with the help of saidleaves.

Among advantage of certain embodiments of the presently disclosedsubject matter is the ability of migrating data from a logical volume toanother logical volume (e.g. related to different filesystems and/ordifferent Virtual Machines), whilst eliminating a need of using hostresources as well as eliminating a need of physically copying data fromone location to the other, thereby reducing consumption of host andstorage resources including the cache and internal bandwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the disclosed subject matter and to see how itcan be carried out in practice, embodiments will now be described, byway of non-limiting example only, with reference to the accompanyingdrawings, in which:

FIG. 1 illustrates a schematic functional block diagram of an exemplarystorage arrangement in accordance with certain embodiments of thepresently disclosed subject matter;

FIG. 2 illustrates a schematic functional block diagram of a controllayer configured in accordance with certain embodiments of the presentlydisclosed subject matter;

FIG. 3 schematically illustrates a non-limiting example of a mappingtree;

FIG. 4 illustrates a generalized flow diagram of a migration process inaccordance with certain embodiments of the presently disclosed subjectmatter;

FIG. 5 schematically illustrates an exemplary mapping of addressesrelated to source and destination logical volumes into addresses relatedto physical storage space in accordance with certain embodiments ofpresently disclosed subject matter;

FIG. 6 illustrates a generalized flow diagram of handling write requestsaddressed to the migrated address range in the source volume inaccordance with certain embodiments of presently disclosed subjectmatter; and

FIGS. 7 a-7 c schematically illustrate the process of write requestshandling detailed with reference to FIG. 6.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresently disclosed subject matter may be practiced without thesespecific details. In other instances, well-known methods, procedures,components and circuits have not been described in detail so as not toobscure the presently disclosed subject matter.

Unless specifically stated otherwise, as apparent from the followingdiscussions, it is appreciated that throughout the specificationdiscussions utilizing terms such as “processing”, “computing”,“calculating”, “determining”, “generating”, “writing”, “selecting”,“allocating”, “storing”, “managing” or the like, refer to the actionand/or processes of a computer that manipulate and/or transform datainto other data, said data represented as physical, such as electronic,quantities and/or said data representing the physical objects. The term“computer” should be expansively construed to cover any kind ofelectronic system with data processing capabilities, including, by wayof non-limiting example, storage system and parts thereof disclosed inthe present applications.

The operations in accordance with the teachings herein may be performedby a computer specially constructed for the desired purposes or by ageneral-purpose computer specially configured for the desired purpose bya computer program stored in a computer readable storage medium.

Embodiments of the presently disclosed subject matter are not describedwith reference to any particular programming language. It will beappreciated that a variety of programming languages may be used toimplement the teachings of the presently disclosed subject matter asdescribed herein.

The references cited in the background teach many principles ofmigrating data in storage systems that are applicable to the presentlydisclosed subject matter. Therefore the full contents of thesepublications are incorporated by reference herein where appropriate forappropriate teachings of additional or alternative details, featuresand/or technical background.

In the drawings and descriptions, identical reference numerals indicatethose components that are common to different embodiments orconfigurations.

Bearing this in mind, attention is drawn to FIG. 1 illustrating anexemplary storage environment in accordance with certain embodiments ofthe presently disclosed subject matter.

The computer system comprises a plurality of host computers(workstations, application servers, etc.) illustrated as 101-1-101-nsharing common storage means provided by one or more virtualized storagesystems. The illustrated storage system 102 comprises a storage controllayer 103 comprising one or more appropriate storage control devicesoperatively coupled to the plurality of host computers and a pluralityof data storage devices 104-1-104-n constituting a physical storagespace optionally distributed over one or more storage nodes. The storagecontrol layer 103 is operable to control interface operations (includingI/O operations) between host computers and the plurality of storagedevices. The storage control layer is further operable to handle avirtual representation of physical storage space and to facilitatenecessary mapping between the physical storage space and its virtualrepresentation. The virtualization functions can be provided inhardware, software, firmware or any suitable combination thereof.Optionally, the functions of the control layer can be fully or partlyintegrated with one or more host computers and/or storage devices and/orwith one or more communication devices enabling communication betweenthe hosts and the storage devices. Optionally, a format of logicalrepresentation provided by the control layer may differ, depending oninterfacing applications.

The physical storage space can comprise any appropriate permanentstorage medium and include, by way of non-limiting example, one or moredisk drives and/or one or more disk units (DUs). The physical storagespace comprises a plurality of data blocks, each data block can becharacterized by a pair (DD_(id), DBA), and where DD_(id) is a serialnumber associated with the disk drive accommodating the data block, andDBA is a logical block number within the respective disk. By way ofnon-limiting example, DD_(id) can represent a serial number internallyassigned to the disk drive by the system or, alternatively, a WWN oruniversal serial number assigned to the disk drive by a vendor. Thestorage control layer and the storage devices can communicate with thehost computers and within the storage system in accordance with anyappropriate storage protocol.

Stored data can be logically represented to a client (e.g. a user, anapplication, etc.) in terms of logical storage devices referred tohereinafter also as logical units, logical volumes or volumes. A logicalunit (LU) is a virtual entity logically presented to a client as asingle virtual storage device. The logical volume represents a pluralityof data blocks characterized by successive Logical Block Addresses (LBA)ranging from 0 to a number LUK. Different LUs can comprise differentnumbers of data blocks, while the data blocks are typically of equalsize (e.g. 512 bytes). Blocks with successive LBAs can be grouped intoportions that act as basic units for data handling and organizationwithin the system. Thus, for instance, whenever space has to beallocated on a disk or on a memory component in order to store data,this allocation can be done in terms of data portions also referred tohereinafter as “allocation units”. Data portions are typically of equalsize throughout the system (by way of non-limiting example, the size ofa data portion can be 64 Kbytes).

When receiving a write request from a host, the storage control layerdefines a physical location(s) for writing the respective data (e.g. alocation designated in accordance with an allocation scheme,preconfigured rules and policies and/or location available for alog-structured storage, etc.) and further processes the requestaccordingly. When receiving a read request from the host, the storagecontrol layer obtains the physical location(s) of the desired data andfurther processes the request accordingly.

Mapping between logical and physical locations of data portions and/orgroups thereof is further detailed with reference to FIGS. 2-7.Addresses related to logical locations can be mapped into addressesrelated to the physical locations with the help of the allocation module105 operable to provide necessary address translation. The allocationmodule can be implemented as a centralized module operatively connectedto the plurality of storage control devices or can be, at least partly,distributed over a part or all storage control devices.

Logical objects (e.g. data files, multimedia files, database tables,filesystems, etc.) stored in a logical volume V_(src) can be migrated tological volume V_(dest). The migration may be useful in scenariosinvolving duplication of virtual hosts or of applications running in avirtual machine environment. In such cases, migration of whole or partof logical volumes may be necessary. Additional scenarios may involveduplicating data for databases backup, filesystem backup, large filecloning, etc.

Optionally, each host can comprise a plurality of virtual machines (notshown). An application from a first virtual machine VM1 running in ahost H_(j) can be migrated to a second virtual machine VM2 running in ahost H_(k). In this case H_(j) and H_(k) could be the same host. Files(or other logical objects) related to the application, currently storedin an associated volume V_(src) and owned by a file system FS1associated with VM1 will be migrated to a file system FS2 associatedwith VM2 and to be stored in volume V2.

The presently disclosed subject matter is not bound by the specificarchitecture illustrated with reference to FIG. 1, equivalent and/ormodified functionality can be consolidated or divided in another mannerand can be implemented in any appropriate combination of software,firmware and hardware. The control layer and/or parts thereof can beimplemented as suitably programmed computer(s).

Referring to FIG. 2, there is illustrated a schematic functional diagramof the control layer configured in accordance with certain embodimentsof the presently disclosed subject matter. The illustrated configurationis further detailed in U.S. application Ser. No. 12/897,119 filed Oct.4, 2010, assigned to the assignee of the present application andincorporated herein by reference in its entirety.

The virtual presentation of the entire physical storage space can beprovided through creation and management of one or more virtualizationlayers. By way of non-limiting example, the illustrated control layercomprises two interconnected virtualization layers: a first virtuallayer 204 operable to represent logical units available to clients(workstations, applications servers, etc.) and characterized by aVirtual Unit Space (VUS); and a second virtual layer 205 interfacingwith the physical storage space via a physical storage interface 203.The logical units are represented in VUS as virtual data blockscharacterized by virtual unit addresses (VUAs). The second virtual layer205 is operable to represent the physical storage space available to theclients and is characterized by a Virtual Disk Space (VDS). By way ofnon-limiting example, storage space available for clients can becalculated as the entire physical storage space less reserved parityspace and less spare storage space. The virtual data blocks arerepresented in VDS with the help of virtual disk addresses (VDAs).Virtual disk addresses are substantially statically mapped intoaddresses in the physical storage space. This mapping can be changedresponsive to modifications of physical configuration of the storagesystem (e.g. because of disk failure or disk addition). The VDS can befurther configured as a concatenation of representations (illustrated as210-213) of RAID groups.

Addresses in VUS can be dynamically mapped into addresses in VDS withthe help of the allocation module 105 operable to provide translationfrom VUA to VDA via Virtual Address Mapping.

By way of non-limiting example, FIG. 2 illustrates a part of the storagecontrol layer corresponding to two LUs illustrated as LUx (208) and LUy(209). The LUs are mapped into the VUS. In a typical case, initially thestorage system assigns to a LU contiguous addresses (VUAs) in VUS.However, existing LUs can be enlarged, reduced or deleted, and some newones can be defined during the lifetime of the system. Accordingly, therange of contiguous data blocks associated with the LU can correspond tonon-contiguous data blocks assigned in the VUS. The parameters definingthe request in terms of LUs are translated into parameters defining therequest in the VUAs, and parameters defining the request in terms ofVUAs are further translated into parameters defining the request in theVDS in terms of VDAs and further translated into physical storageaddresses.

Translating addresses of data blocks in LUs into addresses (VUAs) in VUScan be provided independently from translating addresses (VDA) in VDSinto the physical storage addresses. Such translation can be provided,by way of non-limiting examples, with the help of an independentlymanaged VUS allocation table and a VDS allocation table handled in theallocation module 105 as further detailed in U.S. application Ser. No.12/897,119. Different blocks in VUS can be associated with one and thesame block in VDS. Optionally, allocation of physical storage space canbe provided only responsive to destaging respective data from the cachememory to the disks (e.g. for snapshots, thin volumes, etc.).

By way of non-limiting example, the Virtual Address Mapping can beprovided with the help of one or more mapping data structures, forexample configured as mapping trees detailed in U.S. application Ser.No. 12/897,119.

A non-limiting example of the mapping structure is illustrated in FIG.3. For purpose of illustration only, the following description isprovided for mapping trie(s) configured to provide mapping between VUAand VDA addresses. It should be noted that mapping between addressesrelated to logical volumes (LBA, VUA) and addresses (VDA, DBA) relatedto the physical address space can comprise at least one of the followingmapping options: mapping between LBA and DBA addresses; mapping betweenVUA and VDA addresses; mapping between LBA and VDA addresses; andmapping between VUA and DBA addresses. When in some following examples aVUA offset is denoted as LBA address, it should be interpreted as VUAaddress corresponding to respective LBA address. Those skilled in theart will further readily appreciate that the presently disclosed subjectmatter is not bound by mapping with the help of mapping trees and can beimplemented, likewise, with the help of any other appropriate mappingstructure (e.g. mapping tables with respective entries and referencestherebetween). The mapping tree can be configured as an ordered tree(trie) data structure comprising one or more leaves wherein a) a depthof a leaf in the tree represents a length of a contiguous range ofaddresses related to a given corresponding logical group; b) a givenpath followed from a tree root to the leaf indicates an offset of therespective range of addresses within the given logical group; c) a valueassociated with the leaf indicates an offset of respective contiguousrange of addresses related to the physical storage space andcorresponding to said contiguous range of addresses related to saidgiven logical group.

The depth of a given leaf can be configured in inverse relation to thelength of respective contiguous range of addresses related to arespective logical group. A sequential number of a given leaf node canbe calculated as D-1, wherein D is equal to a maximal admissible numberof addresses related to the physical storage space divided by a numberof contiguous addresses in the range of addresses related to the logicalgroup.

The path followed from a tree root to the leaf can be represented as astring of zeros and ones depending on right and/or left branchescomprised in the path. The offset of the respective range of addresseswithin the given logical group can be calculated in accordance with thepath followed from the tree root to the leaf with the help of thefollowing expression:

$\sum\limits_{i = 0}^{d - 1}{r_{i} \cdot 2^{({M - i - 1})}}$where M is the power of two in the maximal number of admissibleaddresses in the given logical group, d is the depth of the leaf, i=0,1, 2, 3, d-1 are the successive nodes in the tree leading to the leaf,and r, is a value equal to zero for one-side branching and equal to onefor another side branching.

The mapping tree can comprise at least one leaf with at least twoassociated values, said associated values indicating offsets of twodifferent contiguous ranges of addresses related to the physical storagespace and corresponding to the same contiguous range of addressesrelated to the logical address space.

As illustrated by way of non-limiting example in FIG. 3, successiveaddresses in VUA can be mapped in several groups of successive VDAaddresses. A data portion 301 in VUA is mapped to four differentportions of successive blocks (302-305) in VDS. Mapping between VUA andVDS addresses is provided with the help of mapping structure 306configured, by the way of non-limiting example as a mapping trie. EachVDS successive block starts at the address specified in the respectiveleaf and has a length corresponding to the depth of the branch, as wasdetailed above.

Bearing the above in mind, attention is drawn to FIG. 4 illustrating amethod of migrating at least one data portion from a source logicalvolume V_(src) to one or more destination logical volumes V_(dest) inaccordance with certain embodiments of the presently disclosed subjectmatter.

Operations detailed with reference to FIGS. 4-7 can be provided with thehelp of the allocation module 105 or one or more modules in the controllayer specially configured for the desired purposes (e.g. migrationmodule, background module, etc.).

The data portion to be migrated (also referred to hereinafter as thesource data portion) is characterized by length LGT_(x) and offsetLBA_(x) in a source logical volume V_(src) and offset LBA_(y) in thedestination volume V_(dest). For purpose of illustration only, it isassumed that the migrated data portion is an extent of file F. The fileF is owned by a filesystem FS_(dest), associated with a logical volumeV_(src). File F is to be migrated to a file system FS_(dest), associatedwith a logical volume V_(dest). If file F spans more than one extent ofsuccessive blocks within V_(src), the respective data portions (extents)can be migrated separately (e.g. one after the other) as part of anatomic operation of migrating the file. By way of non-limiting example,the migrated data portion can be an extent of a file F stored in volumeV_(src) related to a file system FS1 associated with a virtual machineVM1, this file to be migrated to volume V_(dest) related to a filesystem FS2 associated with VM2 running on the same host.

Those skilled in the art will readily appreciate that the presentlydisclosed subject matter is not bound by migration of file extentsand/or migration in virtual machine environment, and can be implemented,likewise, for migration of data portions and groups thereof belonging toany logical objects from a source logical volume to a destinationlogical volume.

Thus, a migration operation comprises migrating a data portion havinglength LGT_(x) and starting at a logical block address LBA_(x) in volumeV_(src) to logical block address LBA_(y) in volume V_(dest). Themigration of data portion can be described by a migration functionMIGRT(V_(dest), LBA_(y), V_(src), LBA_(x), LGT_(x)). The range in thedestination volume with offset LBA_(y) and length LGT_(x) is referred tohereinafter as a destination range.

In conventional art, migration of data portions between logical volumescan be provided with the help of the host (e.g. application runningtherein) which can read the respective data from the volume V_(src) andwrite it into volume V_(dest). Alternatively, as known in theconventional art, the migration can be performed by physical copyingdata from the location currently allocated to V_(src) to locationcorresponding to V_(dest), and redefining the meta-data accordingly,such copying provided without a host involvement.

The technique provided in accordance with certain embodiments of thecurrently presented subject matter, enables virtual copying of thesource data portion from logical volume V_(src) to logical volumeV_(dest) with neither need in physical copying any data nor need in hostinvolvement in the migration process. The virtual copying can beprovided with or without keeping the source instance of the dataportion.

In accordance with certain embodiments of the presently disclosedsubject matter, the storage control layer is configured (401) tocomprise a source mapping data structure DS_(src) assigned to the sourcelogical volume V_(src). The source mapping data structure is configuredto map between one or more contiguous ranges of addresses related to thesource logical volume and one or more contiguous ranges of addressesrelated to corresponding physical address space. The source datastructure comprises at least one entry corresponding to a source logicaladdress range associated with data portions (extents) to be migrated andindicative of respective ranges of addresses related to the physicaladdress space and corresponding to the data portions. By way ofnon-limiting example, the source mapping data structure can beconfigured as an ordered tree TR_(src) comprising one or more leaves(entries) corresponding to the data portion to be migrated. The valuesassociated with these leaves indicate respective ranges of addressesrelated to the physical address space and corresponding to the dataportion to be migrated.

The storage control layer is further configured (402) to comprise adestination mapping data structure DS_(dest) assigned, respectively, tothe destination volume V_(dest). The destination mapping data structureis configured to map between one or more contiguous ranges of addressesrelated to the destination logical volume and one or more contiguousranges of addresses related to the corresponding physical address space.

Responsive to a migration command, the destination mapping datastructure DS_(dest) is configured (403) to comprise an entry thatincludes a destination logical address range associated with themigrated data portion and a reference to the source data structure,wherein the reference comprises an indication of the source logicaladdress associated with the source data portion in the source logicalvolume V_(scr) before migration. Thus a request related to the migrateddata portion in the destination volume will be addressed (404) by thedestination mapping data structure DS_(dest) to the respective entry inthe source mapping data structure DS_(src) capable of furthertranslating the request into addresses related to physical addressspace. Upon receiving an I/O request addressed to the migrated dataportion in the destination volume V_(dsts), the destination mapping datastructure DS_(dest) is looked up by the destination logical address toretrieve a reference to the source data structure indicative of thesource logical address. In the source mapping data structure DS_(src),the source logical address associated with the source data portion isfurther looked up to retrieve the actual physical address. Thus, thesource data portion is virtually copied to the destination logicalvolume.

The destination mapping data structure can be configured as an orderedtree TR_(dest) configured to map between one or more contiguous rangesof addresses related to the destination logical volume and one or morecontiguous ranges of addresses related to corresponding physical addressspace. Responsive to a migration command, the destination mapping treeTR_(dest) is configured to include a leaf corresponding to the migrateddata portion, wherein a value associated with said leaf indicates thesource logical volume V_(scr) and the offset of the data portion thereinbefore migrating. Thus, a request related to the migrated data portionand received by a destination mapping tree TR_(dest) will be addressedto the source mapping tree TR_(src) according to the value associatedwith the leaf. The source mapping tree will provide further translatingthe request into addresses related to physical address space.

Likewise, if the source data portion needs to be migrated to severaldestination volumes, the operations above are provided for eachdestination volume and associated data structures. Optionally, migrationto multiple destination volumes can be provided as a single atomicoperation.

It shall be noted that the disclosed operation of migrating a dataportion between logical volumes can be considered as a virtual migrationas it does not alter addresses corresponding to the data portion andrelated to the physical address space.

FIG. 5 schematically illustrates an exemplary mapping of addressesrelated to source and destination logical volumes into addresses relatedto physical storage space, and further details the migration operationdetailed with reference to FIG. 4.

The source logical volume V_(src) (501) is provided with assignedmapping tree TR_(src) (503) configured to map, at least, betweencontiguous ranges of addresses related to the data portion 505 in thesource logical volume and ranges of addresses related to correspondingphysical address space. The data portion 505 is characterized by offsetLBA_(x) and length LGT_(x). The exemplified mapping tree TR_(src)comprises four leaves, the values associated with these leaves indicaterespective ranges of addresses related to the physical address space andcorresponding to the data portion.

The destination logical volume V_(dest) (502) is provided with assignedmapping tree TR_(dest) (504) configured to map, at least betweencontiguous ranges of addresses related to the data portion 506 in thedestination logical volume and ranges of addresses related tocorresponding physical address space. The data portion 506 is the dataportion 505 upon migration to the destination logical volume. The dataportion 506 is characterized by offset LBA_(y) and length LGT_(x).

Responsive to a migration command MIGRT (V_(dest), LBA_(y), V_(src),LBA_(x), LGT_(x)) the destination mapping tree TR_(dest) is configuredto include a leaf 507. This leaf corresponds to the migrated dataportion with the offset LBA_(y) and the length LGT_(x), and the valueassociated with said leaf indicates the source logical volume V_(scr)and the offset LBA_(x) of the data portion 505 before migrating.

Optionally, the migrated data portion can replace data comprised in thedestination volume prior to receiving the migration command MIGRT(V_(dest), LBA_(y), V_(src), LBA_(x), LGT_(x)) and mapped by thedestination mapping tree TR_(dest) accordingly. In this case, uponreceiving the migration command, the mapping tree is reconfigured sothat the leaf 507 replaces any other leaves related to the data rangecharacterizing the migrated data portion with the offset LBA_(y) and thelength LGT_(x).

A read request READ (V_(dest), LBA_(y)+K, P) addressed to a data rangewith length P and offset K within the migrated data portion 506, will beserved with the help of the destination mapping tree 504. The referencein the leaf 507 addresses to the source mapping tree TR_(src) forfurther translation. The source mapping tree TR_(src) will provideaddresses related to physical address space and corresponding to datarange LBA_(x)+K, P in the data potion 505 before migration todestination logical volume.

Thus, the data portion 505 has been virtually migrated from the sourcelogical volume to the destination logical volume in a single, atomicoperation, by means of a mere manipulation of metadata and withoutphysical copying of data in the storage system.

Those skilled in the art will readily appreciate that, likewise, thedisclosed process can be implemented upon receiving a merge requestMERGE (Vdest, LBAy, Vsrc, LBAx, LGTx) if Vdest already contain data inthe destination range when the data migration operation is initiated.

Mapping between addresses in a destination logical volume and addressesrelated to physical address space with the help of referenced datastructure assigned to a source logical volume is referred to hereinafteras indirect mapping. A process of serving a request with the help ofindirect mapping is referred to hereinafter as indirect addressing.

It shall be noted that in accordance with certain embodiments of thepresently disclosed subject matter, a move command can be provided in amanner similar to the described above with regard to the migrationcommand. Responsive to a move command MOVE (V_(dest), LBA_(y), V_(src),LBA_(x), LGT_(x)), there is provided an atomic operation comprisingindirect mapping the migrated data portion to the addresses related tophysical address space with the help of at least one entry associatedwith the source data portion in the source mapping data structure, andconfiguring this entry in the source data structure DS_(src) to bear aspecial mark indicative that the entry (e.g. the leaf in the mappingtree) is unavailable to a client.

Referring to FIG. 6, there is illustrated a generalized flow diagram ofhandling write requests addressed to the source data portion in thesource volume.

In certain embodiments, there can be a need to keep and independentlyupdate the source data portion along with the migrated data portion.

In accordance with certain embodiments of the presently disclosedsubject matter, the mapping data structures in the source and in thedestination volumes are further configured (601) to bear an indicationof a number of mapping trees indirectly mapping a given data portion indifferent logical volumes to the same contiguous range of addressesrelated to physical address space. This indication, indicative for agiven extent of the number of separate instances of the extentindirectly mapped to the addresses related to physical address spacecorresponding to the extent is referred to hereinafter as multiplereference indication (MRI). The indication can be provided with the helpof a reference counter associated with the source volume and one or moredestination volumes and/or data portions in the volumes. The referencecounter can be implemented as a separate data structure or, fully orpartly, integrated with respective mapping data structures. By way ofnon-limiting example, the MRI value can be assigned to each leafcorresponding to the given extent in source and destination mappingtrees, and be updated upon extent modification(s).

For a given extent, the reference counter is indicative of, at least,all leaves in the source tree bearing indication that there is at leastone destination tree TR_(dest) mapping respective data portions to thesame contiguous range of addresses related to physical address space.The reference counter can further comprise a data structure (e.g. atable) having entries corresponding to the extents and indicative of theMRI value. For example, the entry can contain the following fields for agiven extent migrated to three destination volumes:

-   -   V_(src); LBA_(x); Length (in blocks or in sections); MRI=3;        V_(dest1), LBA_(y1); V_(dest2), LBA_(y2); _(Vdest 3), LBA_(y3);        etc.

When a given extent is migrated to a first destination volume, acorresponding entry is added to the table with the MRI=1 in MRI valuefield. Every time the given extent is migrated, the MRI value in thecorresponding entry in the table is updated to indicate the amount ofindirectly mapped separate instances of the given extent. Optionally,the reference counter table can include only entries with non-zero MRIvalue. As will be further detailed with reference to FIGS. 6-7, the MRIvalue is decreased responsive to modification of one of the instances.When MRI value reaches zero, the respective entry can be deleted fromthe table.

For purpose of illustration only, the following description is providedfor write requests addressed to the address range in the source volumecorresponding to the entire extent migrated to a single destinationvolume. Those skilled in the art will readily appreciate that thepresently disclosed subject matter can be implemented, likewise, whenthere are several instances of the extent migrated to severaldestination volumes.

Upon receiving by the source volume a write request WRITE (V_(src),LBA_(x), LGT_(x)), the following steps 602-607 are provided as a singleatomic operation, i.e. operation that either succeeds or fails in itsentirety and not in a partial way. The atomic operation comprises:

-   -   assigning a new contiguous range of addresses related to        physical address space for the new data to be destaged (602) and        associating the range of physical addresses to the corresponding        virtual address range in the source mapping data structure;    -   decreasing MRI value in the reference counter table entry        corresponding to the extent (V_(src), LBA_(x), LGT_(x)) from one        to zero (and, optionally, removing the entry as MRI=0) (603);    -   changing the value of the leaf corresponding to the migrated        extent in the destination mapping tree TR_(dest) by replacing        the reference to the source volume with the physical address        range corresponding to the extent in the source mapping tree        TR_(src) (604);    -   decreasing MRI value in the leaf corresponding to the extent in        the destination mapping tree TR_(dest) from one to zero (605);    -   changing the value of the leaf corresponding to the migrated        extent in the source mapping tree TR_(srct) by replacing the        physical address range with the new physical address range        assigned at step 602 (606);    -   decreasing MRI value in the leaf corresponding to the extent in        the source mapping tree TR_(src) from one to zero (607).

In the illustrated case of a single destination volume, upon completingthe atomic operation, the indirect mapping has been removed and eachmapping tree points to respective different physical address ranges.

Those skilled in the art will readily appreciate that, likewise, thedisclosed process can be implemented upon receiving a delete requestDELETE (V_(src), LBA_(x), LGT_(x)) for deleting the extent from thesource volume V_(src) after migration. Steps 602, 606 and 607 can bereplaced by deleting the respective leaf in the source mapping treeTR_(srct).

In a case of several instances of the extent migrated to severaldestination volumes, additional care can be taken, upon overwriting themigrated extent in the source volume, for keeping the value of theoffset related to the physical address space corresponding to the extentbefore migration, as well as for keeping the related metadata. By way ofnon-limiting example, step 604 can be modified so that the destinationmapping tree TR_(dest) in a first destination volume V_(dest) isconfigured to point to the physical address range copied from theTR_(src). Leaves corresponding to other instances of the migrated extentshall be re-configured to refer to the first destination volume V_(dest)instead of the source volume V_(src), and MRI values updatedaccordingly. The entry corresponding to the extent can be removed fromthe reference counter table only when MRI becomes equal to zero. By wayof alternative non-limiting example, the respective leaf in the sourcetree can bear the value of the old offset in addition to the value ofthe updated offset. In this case the old value is marked to be used onlyfor indirect mapping for responses received from the destinationvolume(s). The old value can be deleted only when the value ofrespective MRI becomes equal to zero.

A write request addressed to the instance in the destination volumeWRITE (Vdest, LBA_(y), LGT_(x)) replaces the reference to DS_(src) inthe destination mapping structure DS_(dest) by the destination physicaladdress allocated for new/overwriting data and reduces respective MRIvalue in the reference counter.

FIGS. 7 a and 7 b schematically illustrate the process detailed withreference to FIG. 6.

FIG. 7 a schematically illustrates the non-limiting example in which theVUA extent 705 in the source volume 701 has the migrated instance 706 inthe destination volume 702. The source mapping tree TR_(src) (703) mapsbetween contiguous range of VUA addresses corresponding to (LBA_(x),LGT_(x)) and VDA addresses related to the extent 705. The exemplifiedmapping tree TR_(src) comprises a single leaf 707 indicative of VDA_(x)of range of VDA addresses corresponding to the extent.

The destination mapping tree TR_(dest) (704) maps between VUA and VDAaddresses related to the migrated extent 706. The exemplified mappingtree TR_(src) comprises a single leaf 708, while the value associatedwith said leaf indicates the source logical volume V_(scr) and theoffset LBA_(x) of the extent 705.

Both leaves 707 and 708 bear MRI value MRI=1, indicating that there isone mapping tree indirectly mapping the instances of the extent to thesame contiguous range of VDA addresses.

FIG. 7 b schematically illustrates the mapping trees illustrated in FIG.7 a and is further modified in response to the write request WRITE(V_(src), LBA_(x), LGT_(x)). Leaf 707 has the new value and points tothe new offset VDA_(xX) of the new contiguous (with length LGT_(x))range of VDA assigned for new data to be destaged. Leaf 708 has thevalue VDA_(x) corresponding to the VDA offset of the extent in thesource mapping tree TR_(src) before modification by the write request.

Both leaves 707 and 708 bear MRI value reduced to zero, indicating thatthere are no mapping trees indirectly mapping the instances of theextent to the same contiguous range of VDA addresses.

Referring now to FIG. 7 c, there is schematically illustrated amodification of the process detailed with reference to FIG. 6 for a caseof a write request addressed to a part of the migrated address range inthe source volume.

Upon receiving a write request WRITE(V_(src), LBA_(x)+K, P) addressed tothe range 715 with offset from LBA_(x)+K and length=P, the sourcemapping tree 703 illustrated with reference to FIG. 7 a is modified atstep 604 to comprise three leaves representing mapping of threedifferent parts of the extent:

-   -   leaf 716 corresponding to the address range from LBA_(x) to        LBA_(x)+K;    -   leaf 717 corresponding to the requested address range from        LBA_(x)+K to LBA_(x)+K+P); and    -   leaf 718 corresponding to the address range from LBA_(x)+K+P to        LBA_(x)+LGT_(x));

Leaves 716 and 718 have VDA values corresponding to VDA addresses VDA₁and VDA₃ originally mapped to the respective ranges. Value in the leaf717 has the new value VDA₂₂ (instead of originally mapped value VDA₂)corresponding to the new location assigned to the requested range in thedestage process.

Likewise, the destination mapping tree 704 illustrated with reference toFIG. 7 a is modified at step 606 to comprise three leaves representingmapping of three different parts of the migrated extent:

-   -   leaf 726 corresponding to the address range from LBA_(y) to        LBA_(y)+K;    -   leaf 727 corresponding to the requested address range from        LBA_(y)+K to LBA_(y)+K+P); and    -   leaf 728 corresponding to the address range from LBA_(y)+K+P to        LBA_(y)+LGT_(x));

Leaves 726 and 728 bear referencing to addresses in the source volumecorresponding to addresses VDA₁ and VDA₃ originally indirectly mapped tothe respective ranges. Leaf 727 has the value VDA_(x) corresponding tothe VDA offset of the requested range in the source mapping treeTR_(src) before modification by the write request.

The reference counter table treats each of the leaves as a separateentry replacing entries corresponding to the extents 705 and 706 beforethe write request. Likewise, the MRI values are treated separately foreach leaf. Leaves 716, 718, 726 and 726 bear MRI value MRI=1, while MRIvalue of leaves 717 and 727 is reduced to zero.

It is to be understood that the presently disclosed subject matter isnot limited in its application to the details set forth in thedescription contained herein or illustrated in the drawings. Thepresently disclosed subject matter is capable of other embodiments andof being practiced and carried out in various ways. Hence, it is to beunderstood that the phraseology and terminology employed herein are forthe purpose of description and should not be regarded as limiting. Assuch, those skilled in the art will appreciate that the conception uponwhich this disclosure is based may readily be utilized as a basis fordesigning other structures, methods, and systems for carrying out theseveral purposes of the presently disclosed subject matter.

It will also be understood that the system according to the presentlydisclosed subject matter can be implemented, at least partly, as asuitably programmed computer. Likewise, the presently disclosed subjectmatter contemplates a computer program being readable by a computer forexecuting the disclosed method. The presently disclosed subject matterfurther contemplates a machine-readable memory tangibly embodying aprogram of instructions executable by the machine for executing thedisclosed method.

Those skilled in the art will readily appreciate that variousmodifications and changes can be applied to the embodiments of thepresently disclosed subject matter as hereinbefore described withoutdeparting from its scope, defined in and by the appended claims.

The invention claimed is:
 1. A method of migrating a source dataportion, the method comprising: receiving, by a storage system, amigration command for migrating the source data portion from a sourcelogical address range within a source logical volume to at least onedestination logical address range within at least one destinationlogical volume; wherein the source logical volume is associated with asource mapping data structure for mapping between first logicaladdresses within the source logical volume and first physical addresseswithin a physical address space of the storage system; wherein thesource mapping data structure comprises at least one first entry formapping between the source logical address range and a physical addressrange that stores the source data portion and belongs to the physicaladdress space; wherein the at least one destination logical volume isassociated with a destination mapping data structure for mapping betweensecond logical addresses within the at least one destination logicalvolume and second physical addresses in the physical address space; inresponse to the migration command, configuring, by the storage system,the destination mapping data structure to comprise at least one secondentry for associating said at least one destination logical addressrange with a reference to said at least one first entry in the sourcemapping data structure, wherein the configuring of the destinationmapping data structure provides at least one migrated data portionwithout physically copying data of the source data; wherein thereference to said at least one first entry is indicative of the sourcelogical address range, wherein the method further comprising, uponreceiving a request related to said at least one migrated data portion:looking up the destination mapping data structure for the at least onedestination logical address range, so as to retrieve the reference tothe at least one first entry; looking up the source mapping datastructure for the source logical address indicated in the reference; andretrieving the physical address range that stores the source dataportion; wherein the method further comprising: responsive to a writerequest for writing new data to said source data portion, providing anatomic operation, said atomic operation comprising: assigning a newrange of addresses related to the physical address space for the newdata to be destaged; updating said at least one first entry in thesource mapping structure to map between the source logical address rangeand said new range of addresses related to the physical address space;and updating said at least one second entry in the destination mappingstructure to map between said at least one destination logical addressrange and the physical address range that was comprised, before theupdating of said at least one first entry, in said at least one firstentry in the source data structure, and removing the reference to the atleast one first entry.
 2. The method of claim 1 wherein the destinationmapping data structure is configured as a destination ordered mappingtree, and wherein said at least one second entry in the destinationmapping data structure is implemented as a leaf of said destinationmapping tree, wherein the method comprising upon receiving the migrationcommand, configuring said leaf to comprise the reference to said atleast one first entry.
 3. The method of claim 2 wherein the sourcemapping structure is configured as a source ordered mapping tree, andwherein said at least one first entry in the source mapping structure isimplemented as a leaf of the source ordered tree, wherein the methodfurther comprising associating the leaf in the source ordered mappingtree and the leaf in the destination ordered mapping tree with amultiple-reference indication indicative of a number of migrated dataportions originated from the source data portion, said portions mappedto addresses related to physical address space with the help of saidleaves.
 4. The method of claim 1, wherein the storage system is coupledto at least one host comprising a plurality of virtual machines andwherein the source logical volume and the at least one destinationlogical volume are associated with different virtual machines.
 5. Themethod of claim 1 further comprising updating the value of amultiple-reference indication associated with said source data portionand with said at least one migrated data portion.
 6. The method of claim1 further comprising: responsive to a request to delete said source dataportion, providing an atomic operation, said atomic operationcomprising: deleting said at least one first entry in the source mappingstructure; updating said at least one second entry in the destinationmapping structure to map between said at least one destination logicaladdress range and the physical address range that was stored the sourcedata portion, before the deleting, and removing the reference to the atleast one first entry.
 7. The method of claim 1 further comprising:responsive to a write request for writing a new data to said at leastone migrated data portion, providing an atomic operation, said atomicoperation comprising: assigning a new range of addresses related to thephysical address space for the new data to be destaged; updating said atleast one second entry in the destination mapping structure to mapbetween said at least one destination logical address range and said newrange of addresses related to the physical address space, and removingthe reference to the at least one first entry; and reducing the value ofthe multiple-reference indication associated with said at least onedestination data portion.
 8. The method of claim 1, wherein migrationoperations for a plurality of source data portions constituting alogical object are provided as a single atomic operation.
 9. The methodof claim 1 wherein the configuring of the destination mapping datastructure provides the at least one migrated data portion withoutaltering addresses related to the physical address space andcorresponding to said source data portion and said at least one migrateddata portion.
 10. A storage system comprising a plurality of physicalstorage devices constituting a physical storage space and controlled bya plurality of storage control devices constituting a storage controllayer, wherein the storage control layer is configured to: receive amigration command for migrating a source data portion from a sourcelogical address range within a source logical volume to at least onedestination logical address range within at least one destinationlogical volume; wherein the source logical volume is associated with asource mapping data structure for mapping between first logicaladdresses within the source logical volume and first physical addresseswithin the physical address space; wherein the source mapping datastructure comprises at least one first entry for mapping between thesource logical address range and a physical address range that storesthe source data portion and belongs to the physical address space; andwherein the at least one destination logical volume is associated with adestination mapping data structure for mapping between second logicaladdresses within the at least one destination logical volume and secondphysical addresses in the physical address space; wherein said storagecontrol layer is further operable to configure, in response to themigration command, the destination mapping data structure to comprise atleast one second entry for associating said at least one destinationlogical address range with a reference to said at least one first entryin the source mapping data structure, wherein the configuring of thedestination mapping data structure provides at least one migrated dataportion without physically copying data of the source data portion;wherein the reference to said at least one first entry is indicative ofthe source logical address range, wherein the storage system is furtherconfigured to, upon receiving a request related to said at least onemigrated data portion: look up the destination mapping data structurefor the at least one destination logical address range, so as toretrieve the reference to the at least one first entry; look up thesource mapping data structure for the source logical address indicatedin the reference; and retrieve the physical address range that storesthe source data portion; wherein the storage system is furtherconfigured to: responsive to a write request for writing new data tosaid source data portion, provide an atomic operation, said atomicoperation comprising: assigning a new range of addresses related to thephysical address space for the new data to be destaged; updating said atleast one first entry in the source mapping structure to map between thesource logical address range and said new range of addresses related tothe physical address space; and updating said at least one second entryin the destination mapping structure to map between said at least onedestination logical address range and the physical address range thatwas comprised, before the updating of said at least one first entry, insaid at least one first entry in the source data structure, and removingthe reference to the at least one first entry.
 11. The system of claim10 wherein the destination mapping data structure is configured as adestination ordered mapping tree, and wherein said at least one secondentry in the destination mapping data structure is implemented as a leafof said destination mapping tree, wherein said leaf is configured, uponreceiving the migration command, to comprise the reference to said atleast one first entry.
 12. The system of claim 11 wherein the sourcemapping data structure is configured as a source ordered mapping tree,and wherein said at least one first entry in the source mappingstructure is implemented as a leaf of the source ordered tree, andwherein the leaf in the source ordered mapping tree and the leaf in thedestination ordered mapping trees are associated with amultiple-reference indication indicative of a number of migrated dataportions originated from the source data portion, said portions mappedto addresses related to physical address space with the help of saidleaves.
 13. The system of claim 10, wherein the storage system iscoupled to at least one host comprising a plurality of virtual machines,wherein the source logical volume and the at least one destinationlogical volume are associated with different virtual machines.
 14. Thesystem of claim 10, wherein the storage control layer is furtherconfigured to, in response to a write request for writing a new data tosaid source data portion: assign a new range of addresses related to thephysical address space for the new data to be destaged; update said atleast one first entry in the source mapping structure to map between thesource logical address range and said new range of addresses related tothe physical address space; and update said at least one second entry inthe destination mapping structure to map between said at least onedestination logical address range and the physical address range thatwas comprised, before the updating of said at least one first entry, insaid at least one first entry in the source data structure, and removethe reference to the at least one first entry.
 15. The system of claim10, wherein the storage control layer is further configured, in responseto a request to delete said source data portion, to: delete said atleast one first entry in the source mapping structure; update said atleast one second entry in the destination mapping structure to mapbetween said at least one destination logical address range and thephysical address range that stored the source data portion before thedeletion.
 16. A computer program product comprising a non-transitorycomputer useable medium having computer readable program code embodiedtherein for migrating a source data portion, the computer programproduct comprising: computer readable program code for causing thecomputer to: receive, by a storage system, a migration command formigrating the source data portion from a source logical address rangewithin a source logical volume to at least one destination logicaladdress range within at least one destination logical volume; whereinthe source logical volume is associated with a source mapping datastructure for mapping between first logical addresses within the sourcelogical volume and first physical addresses within a physical addressspace of the storage system; wherein the source mapping data structurecomprises at least one first entry for mapping between the sourcelogical address range and a physical address range that stores thesource data portion and belongs to the physical address space; whereinthe at least one destination logical volume is associated with adestination mapping data structure for mapping between second logicaladdresses within the at least one destination logical volume and secondphysical addresses in the physical address space; configure, in responseto the migration command, the destination mapping data structure tocomprise at least one second entry for associating said at least onedestination logical address range with a reference to said at least onefirst entry in the source mapping data structure, wherein theconfiguring of the destination mapping data structure provides at leastone migrated data portion without physically copying data of the sourcedata portion; wherein the reference to said at least one first entry isindicative of the source logical address range, wherein the computerreadable program code if for causing the computer to, upon receiving arequest related to said at least one migrated data portion: look up thedestination mapping data structure for the at least one destinationlogical address range, so as to retrieve the reference to the at leastone first entry; look up the source mapping data structure for thesource logical address indicated in the reference; and retrieve thephysical address range that stores the source data portion; wherein thecomputer readable program code if for causing the computer to responsiveto a write request for writing new data to said source data portion,provide an atomic operation, said atomic operation comprising: assigninga new range of addresses related to the physical address space for thenew data to be destaged; updating said at least one first entry in thesource mapping structure to map between the source logical address rangeand said new range of addresses related to the physical address space;and updating said at least one second entry in the destination mappingstructure to map between said at least one destination logical addressrange and the physical address range that was comprised, before theupdating of said at least one first entry, in said at least one firstentry in the source data structure, and removing the reference to the atleast one first entry.